Biological sewage treatment apparatus of the rotary disc type

Claim 1

A sewage treatment apparatus comprising: a rotary shaft; a plurality of holding members fixedly mounted on said rotary shaft for rotation therewith, each of said holding members having a plurality of circumferentially spaced depressed portions at equal distances from the axis of rotation of said shaft; a plurality of rotary plates spaced axially along said shaft and being adapted to be rotated for being partly dipped in sewage in a treating tank; at least some of said rotary plates having at least one projecting portion on the radially inner end thereof complementary in shape to said depressed portions in said holding members, each of said rotary plates with the projection thereon having said inner end fixedly held between two adjacent holding members with the projecting portion engaged in a corresponding depressed portion of one of the two holding members and any remaining rotary plates having no projections thereon being held between a rotary plate and the other of the two holding members; said holding members further having projecting portions thereon on the opposite sides thereof from said depressed portions and having flat portions between the depressed portions, the flat portions on one side being in positions corresponding to depressed portions on the other side, and said rotary plates having depressed portions on the opposite sides thereof from said projecting portions, the lastmentioned projecting portions on said holding members being engaged with said lastmentioned depressed portions on said rotary plates, said rotary plates having no projections thereon being between the sides of said rotary plates on the opposite side from which said projecting portions project and said flat portions on the next adjacent holding members; and said holding members and rotary plates having small holes therein which are aligned when the holding members and rotary plates are assembled, and the material of said holding members and said rotary plates being melt-bonded to each other around the peripheries of said holes.